This research program aims to investigate a role for the beta-subunit of phosphodiesterase (PDE) in photoreceptor degeneration of rcd1 Irish setter dogs; a role for phosducin in photoreceptor development and a role for 2A phosphatase in the process of photoreceptor degeneration. First, our investigation of the rcd1 disorder is based on the hypothesis that a genetic abnormality triggers the accumulation of cGMP through a dysfunction of the cascade PDE. Support for this idea comes from our findings that the rod PDE complex is absent in immature rcd1 photoreceptors and that the beta-PDE subunit does not amplify normally by PCR. A biochemical and molecular biological approach is proposed whereby the genetic lesion in the beta-PDE or other related mRNAs can be identified and characterized. Second, the early expression of phosducin and Tbetatau in developing mouse photoreceptors precedes the terminal differentiation of photoreceptor cells by about a week as evidenced by outer segment formation, synaptogenesis and coordinated accumulation of transducin, PDE and opsin. A role for phosducin or phosducin/betatau in intracellular signaling is suggested by sequence analysis and identification of its conserved domains (GAP, IRA 1 & 2, ankyrin). Deletion and site-specific mutagenesis will be used to define relevant domains within phosducin for betatau subunit binding and to identify phosducin homologues by PCR. Third, 2A phosphoprotein phosphatase has proven metabolic and gene-suppressor activities, and a comparable disruption of phosphorylation/dephosphorylation is proposed in photoreceptor degeneration of rd mice and rcd1 setters. High levels of 2A phosphoprotein phosphatase activity in rd mice retinas leads to protein hypo-phosphorylation, as evidenced by opsin. With our retinal 2A phosphatase antibodies and cDNA, we propose to characterize the retina 2A phosphatase and to evaluate a relationship between cGMP accumulation and 2A phosphatase activity in the mice and setter disorders. It is envisioned that a systematic study of these inherited retinal disorders will provide a fuller understanding of the respective genetic defects and of the mechanisms leading to photoreceptor degeneration.